1. Field of the Invention
The invention relates to a process and an apparatus for the biological treatment, in particular composting, of biogenic and abiogenic substances and/or mixture of substances in a clamp in the presence of biologically active components, in particular microorganisms, in a closed reactor having a plurality of reactor zones.
2. Description of the Related Art
Such processes and plants are known, for example as industrial composting processes and composting plants in a very wide range of embodiments. The rotting, i.e. composting, of biogenic organic and abiogenic substances under aerobic conditions results in the formation of heat and metabolic gases which have to be removed via aeration (ventilation) systems. Usually, fresh air flows through the rotting mixture and the corresponding waste air is blown out. Oxygen is introduced in an uncontrolled manner with the fresh air supply, and moisture and heat are removed with the waste air. Gas, humidity and/or temperature gradients result which cannot be influenced and, owing to the network of operating and process parameters, are suitable only for describing the process.
Thus, important process aims cannot be achieved by means of these conventional aeration systems. If water discharge is desired, heat is thus simultaneously removed in an uncontrolled manner. Thus, on the one hand the desired moisture contents cannot be maintained and on the other hand important predetermined temperatures for the development of mesophilic and thermophilic microflora cannot be independently controlled. It is also not possible to influence the microbial conversion of substances by means of a defined oxygen feed. The deficiencies of the current process controls are evident in the problem of establishing reproducible and specific conditions in the medium, for example in the formation of excessively high temperature plateaus in certain treatment phases, in an undesired dry stabilization of the rotting material and in an unsatisfactory conversion. The discharge of odoriferous substances and production condensate, which necessitate additional treatment means, are further aspects. Since the key parameters of the biological process control, the oxygen supply, the temperature and the moisture content, can be only inadequately maintained, no improvement in the rotting process is achieved even by connecting separate reactors to a central air preparation means, especially since the contents of the reactors exhibit different degrees of rotting and are supplied with identical air quality and quantity of air.
A basic aspect in the further development of the composting process is to improve the unsatisfactory and incorrect use of the potential performance of specific microflora, to remedy the inevitably poor reproducibility of desired qualities as defined by the quality guidelines for composts and/or to prevent the formation of pockets of harmful flora in composts and to prevent their secondary products and to improve the cost-efficiency of the rotting process by optimum process control. The risks of possible harmful effects in the diversified use of composts are otherwise incalculable and are unacceptable against the background of product liability.
DE-40 21 868 A1 - HERHOF - discloses a process for the composting of wastes. The material to be rotted is introduced into a closed container and microbially degraded with a supply of air. To start the composting rapidly and reliably, the waste air emerging from the rotting material is recycled to the rotting material during the initial phase. This air circulation phase is discontinued as soon as the oxygen content falls below 18%. The air circulation system described in this publication serves for conserving the biogenically formed heat, especially in winter.
DE-40 21 865 A1 - BERHOF - likewise describes a process and an apparatus for composting wastes with air circulation. The air circulation serves for maintaining hygienic conditions over a period of 5 days. It is started only after the degradation of the readily degradable components because the biogenic heat formation in the vigorous initial phase of the treatment then cannot be controlled by the system described if it is used for regulating the gas balance. Cooling can be achieved only by means of the fresh air supply as part of an undefined set of parameters.
Finally, DE-40 08 104 A1 - WIENECKE - describes a composting system which is suitable only for small containers since the aeration employs only convection. Control of microbial conversion is not possible.
In the case of these composting plants which have already been realized in practice (DE 40 21 868 A1; DE 40 21 865 A1; DE 40 08 104 A1), the air circulations described are those which are conceptually derived from process engineering which operates only with fresh air and which (from a lack of knowledge) does not utilize the possibilities offered by predetermined climatic conditions. Thus, importance is preferably attached to optimum oxygen supply (21%) in the gas phase, which supply can be achieved with a relatively low air throughput per unit volume and unit time. Frequently, the process relies on the carbon dioxide concentration as a control parameter, which is nonsense in the case of rotting mixtures whose pH is above 7. The attempt to achieve temperature plateaus which are as high as possible rules out the desire to regulate the temperature in the rotting mass to the biologically required conditions for desired conversions as an indispensable condition. However, where this route is adopted, it is found that the air throughput rates are set much too low to create homogeneous conditions in the substrate.
The composting plant stated at the outset is disclosed in DE 40 34 400 A1 or the corresponding WO 92/07807 - GRABBE. In order to avoid repetitions, this document is hereby incorporated by reference. It describes a process for the biotechnological treatment of a mixture of residues, preferably in the form of a clamp, by a microbial conversion process in a closed system which is suitable in particular for the production of compost. Here, physical, chemical and biological process parameters are included in the process control and together tailored to the microbial conversion required for this purpose in each case, with optimization of the hygienization, odor elimination and continuous humus formation of the mixture of residues. For this purpose, the mixture of residues is subjected to two different aeration methods or a mixed form of these two aeration methods. In one aeration method, air is passed through the mixture of residue. In the second aeration method, on the other hand, the air is passed along above the mixture of residues. In order to establish desired temperature conditions, humidity conditions and/or oxygen/carbon dioxide ratios, in particular profiles, in the mixture of residues, the two aeration methods are adapted to one another in such a way that variable mixing ratios between 0 and 100% can be generated from the circulated air volume flow rate. The means for aeration are in each case fans, one fan passing the air along above the mixture of residues and a second fan blowing the air through the mixture of residues.
The process described in the last-mentioned publications (DE 40 34 400 A1, WO 92 07807) usually operates successfully. However, problems may occur when the density of the mixture being rotted hinders flow through the mixture. In the limiting case where the mixture being rotted is impermeable to air, the fan provided for ensuring flow through the mixture merely builds up a static pressure under the clamp without it being possible to cause the air to flow, not even when both fans are running, i.e. the fan provided for ensuring flow over the clamp supports the fan provided for ensuring flow through the clamp, in that the air passing along the top of the clamp has a certain suction action on the clamp. Although both fans are running, only the air flowing over the clamp causes a certain air circulation in the system.
Further patent applications of the applicant (German patent applications with application numbers P 42 15 269.0-41 and P 42 15 267.4 and PCT applications with the application numbers PCT/EP93/01142 and PCT/EP93/01143), which have not yet been laid open, describe variable air circulation systems in closed rotting means for compost production, which eliminate the obvious disadvantages of the conventional systems. They additionally have the advantage that the relevant process parameters can be controlled independently of one another and can be combined in a suitable manner for optimizing the process control. In contrast, these parameters mutually influence each other in the conventional systems and hinder the biological process. The disclosure content of the above patent applications is hereby expressly also declared to be part of the description of the present application.